Cotton plants having a variety of different seed characteristics are known. Of particular interest are cotton plants having so-called naked seeds, seeds from which all the lint can be easily removed during ginning without breaking the fibers or creating seed coat fragments.
Naked seeds have a number of advantages over fuzzy seeds (which retain a fuzz of very short fibers even after ginning). First, naked seeds can be ginned by Roller Gins which cause less damage or tearing to the lint during ginning, thereby retaining the original length of the lint fibers. Second, the less fuzz on the seed, the more efficient the ginning process. This is due to the fact that the fuzz creates resistance to the roller gin during ginning. Therefore, varieties having fuzzy seeds are generally ginned by Saw Gins, which tend to hear the fibers, thus reducing the length and quality of the lint.
The third factor is the ease of removal of lint fibers from the seed. Naked seeds generally require lower force to remove the fibers than fuzzy seeds. Greater resistance to ginning can lead not only to torn fibers, but also to a broken seed coat, especially when the seeds have a relatively weak coat. This causes contamination of the lint with seed coat fragments during removal of the lint. This seed coat fragmentation is minimal in naked seeds.
Several genes are known to control the presence or absence and quantity of fuzz, whose effects are influenced by other genes, so-called modifiers, on the genome. Two of them will be discussed herein. The first is the recessive gene n.sub.2 n.sub.2. This gene is characteristic of most of the commercial cotton varieties of the species G. barbadense. Here, due to the recessive nature of the gene, the naked seed characteristics result only in a variety homozygous for the recessive allele of this gene. In these strains, generally there is substantial lint, i.e., above 30%, and the seed cotton can be ginned by a roller gin. The seeds are never totally naked, but retain fuzz at least at the tip. In some cases, the amount of fuzz remaining on the seed, especially on the chalazal end, causes some tearing of the seed coat during ginning. Furthermore, the seeds are not homogeneous, in that those which are formed higher up on the plant are more naked than those which were formed on lower branches. These strains are also problematic with regard to planting, since all the fuzz must be removed from the seed in order to plant it using conventional planting machines.
The other gene is the dominant gene N.sub.1. This gene is much less common, but its results are more powerful. When the strain is homozygous N.sub.1, the most advantageous results in terms of a naked seed are produced. The presence of four dominant alleles of N.sub.1 results in a totally naked seed, even at the tip, sometimes called a fuzzless seed. And the seeds are homogeneous, in that all the seeds on the plant have the same characteristics. However, this has a corresponding disadvantage in that the quantity of lint is extremely limited, i.e., generally between 0 and 15%, so that such a strain is not commercially viable.
Today, known varieties of cotton (except hybrids) are all homozygous, in order to provide uniformity of the variety. Thus, utilization of the gene N.sub.1 is basically impossible due to the low quantity of lint, regardless of the total genetic background, in most cases. The search for such a strain or variety with high lint percent would be a long and difficult process and not likely to be successful.
Furthermore, in developed countries, so far the obstacles to seed production of cotton hybrids have ruled out the possibility of developing commercial hybrids and utilizing genes in the heterozygous state for commercial purposes. This has only been done in India, where all the crossing is done by hand.